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ENGR5003 / Week 6
ENGR263 2025 Q1(c)Past paperOld spec ENGR2632:223 marks14 min

ENGR263 Mass Transfer Summer 2025 Q1(c) (same question as ENGR263 2021 A3(a))[PARTIAL] official answers Left out: Q1(a) relative volatility (15 marks) and Q1(b) azeotropic vs extractive distillation (10 marks) are distillation, which is not on the current ENGR5003 or ENGR5002 syllabus. Only the Raoult's-law part (c) is converted.

[Q1(a)-(b), on relative volatility and azeotropic / extractive distillation, are not on the current syllabus and are omitted. The same part (c) was set as ENGR263 2021 A3(a), 8 marks.]

Formulas you may need
  • Raoult's law (ideal liquid, ideal vapour): yiP=xiPisaty_iP = x_iP_i^{sat} (learn this)
  • Dalton: P=∑ipiP = \sum_i p_i, yi=pi/Py_i = p_i/P (learn this)
  • Bubble point of a binary at fixed PP: xAPAsat+(1−xA)PBsat=Px_AP_A^{sat} + (1 - x_A)P_B^{sat} = P (learn this)
  • 1 atm=760 mm Hg1\ \mathrm{atm} = 760\ \mathrm{mm\,Hg} (on the formula sheet)
  1. (c)
    Calculate the composition of the vapour phase in equilibrium at 60∘C60^\circ\mathrm{C} with a liquid mixture consisting of 40% mol benzene and 60% mol toluene. Also, determine the composition of a mixture of benzene and toluene that will boil at a temperature of 90∘C90^\circ\mathrm{C} under a pressure of 760 mm Hg. Liquid mixtures of benzene and toluene obey Raoult's Law. The saturated vapour pressures of benzene and toluene at 60∘C60^\circ\mathrm{C} are 385 mm Hg and 140 mm Hg, respectively. At 90∘C90^\circ\mathrm{C}, these values are 1013 and 408 mm Hg, respectively.
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